(Not Applicable)
The invention relates generally to epitaxial metal oxide buffer layers on metal substrates and articles made therefrom. More specifically, the invention relates to a process for depositing electrically conductive oxide epitaxial layers on textured metal substrates, and articles made therefrom.
Epitaxial metal oxide buffer layers on substrates with crystalline, polycrystalline, or biaxially-textured metal surfaces are potentially useful where an electronically active layer is deposited on the buffer layer. The term xe2x80x9cepitaxialxe2x80x9d is used herein and understood by those skilled in the art to mean the growth (method) and placement (apparatus) of a crystalline substance on a crystalline substrate, where the crystalline substance formed follows the crystallographic orientation of the crystalline substrate. Epitaxial crystal growth advantageously permits the formation of crystallographic layers having a high level of crystallographic correlation with respect to an underlying crystalline substrate layer, permitting the formation of improved devices.
The electronically active layer may be a superconductor, a semiconductor, a ferro-electric or an opto-electric material. For example, a biaxially-textured superconductor article to be used for power transmission lines has a multi-layer composition 10, as in FIG. 1. Such deposited superconductor articles most commonly consist of a biaxially-textured metal surface 12, a plurality of buffer layers 14, 16, and a superconducting layer 18. The biaxially-textured metal surface 12, most commonly formed from Cu, Ag, Ni, or Ni alloys, provides support for the superconductor article, and can be fabricated over long lengths and large areas. Epitaxial metal oxide buffer layers 14, 16 comprise the next layers in the superconductor article. The buffer layers 14, 16 are commonly formed from Y2O3 or CeO2, and serve as chemical barriers between the metal surface 12 and the last layer, the last layer being superconducting layer 18.
Current materials research aimed at fabricating improved high-temperature superconductor articles is largely focused on epitaxial growth of high-temperature superconducting layers on biaxially-textured metal surfaces. A biaxially-textured article can be defined as a polycrystalline material in which the crystallographic in-plane and out-of-plane grain-to-grain misorientatioris are small (typically less than 20 degrees) but finite (typically greater than 2 degrees). Superconducting articles with current densities (Jc) in excess of 0.1 MA/cm2 at 77 K have been achieved for epitaxial YBa2Cu3O7 films on biaxially-textured Ni or Ni-based alloy surfaces with the use of certain epitaxial buffer layer constructs between the metal surface and the superconducting layer. In previous work, the synthesis of high-temperature superconductor layers capable of carrying a high (at least 0.1 MA/cm2 at 77 K) Jc has required the use of complex, multilayered buffer architectures.
In order to realize a high-temperature superconducting layer, such as YBa2Cu3O7, possessing a Jc greater than approximately 0.1 MA/cm2 at 77 K on a biaxially-textured metal substrate, the buffer layer architecture should be epitaxial relative to the metal substrate and crack-free. Most preferably, the grains of the buffer layer should be crystallographically aligned perpendicular to the plane of the metal substrate (c-axis oriented) and parallel to the plane of the metal substrate (a-b alignment).
Formation of superconductor articles with this orientation begins with the selection of the metal surface 12. The crystallographic orientation of the metal surface 12 is preferably maintained in the buffer layers 14, 16 and the superconducting layer 18, to the maximum extent possible. Numerous conventional processes are currently being used to grow buffer layers 14, 16 on a metal substrate 12. These processes include vacuum methods, such as pulsed laser deposition, physical vapor deposition electron beam evaporation and sputtering. Also, non-vacuum deposition processes, such as chemical solution deposition and chemical vapor deposition can be used for this purpose.
In addition to being epitaxial relative to the biaxially-textured metal surface, buffer layers 14, 16 are preferably chemically compatible with both the metal surface and superconductor, and mechanically robust so as to prevent microscopic crack formation in the high-temperature superconducting layer and the buffer layers. Prior to the present invention, buffer layers that met these objectives have required multilayer combinations of various oxides.
For example, CeO2 has been used to nucleate an epitaxial (001) oriented oxide layer on a biaxially textured (100) Ni surface However, CeO2 films of over 100 nm thickness form cracks on {100} less than 001 greater than  textured Ni substrates due to significant differences in the thermal expansion coefficients of the oxide film and the Ni substrate. Cracking has prevented utilization of CeO2 as a single buffer layer.
Also, YBCO films grown directly on a YSZ buffer layer on Ni substrates result in two in-plane orientations. This is due to the lattice mismatch between YBCO and YSZ layers. This generally prevents use of YSZ as a single buffer layer.
An additional buffer layer, such as an epitaxial yttria-stabilized zirconia (YSZ) buffer layer on a CeO2 buffer layer has been used to achieve substantially crack-free superconductor articles. The architecture of YBCO/CeO2/YSZ/CeO2/Ni has been the standard architecture for the rolling-assisted biaxially textured substrate (RABiTS) based YBCO coated conductors. In this arrangement, the superior mechanical properties of the YSZ layer substantially circumvent the microcracking problem, and enable the formation of superconducting layers with a high Jc. The CeO2 layer serves primarily to nucleate a (001) oriented epitaxial oxide on the metal surface.
An alternative multi-layer buffer layer uses conducting SRO (SrRuO3 or Sr2RuO4) and LNO (LaNiO3)buffer layers to form YBCO/SRO/LNO/Ni. The suppression of superconducting critical temperatures (Tc) of 75-80 K for YBCO films grown directly on LNO buffers has prevented the use of LNO as the single buffer layer. Also, the preparation of both SRO and LNO target materials are extremely difficult.
Though effective in forming a high Jc superconductor article, the use of a multilayer buffer architecture, as opposed to a single layer buffer architecture, increases the complexity of the superconductor article fabrication process. Using multiple buffer layers typically requires the use of additional raw materials, as compared to a single buffer layer architecture. In addition, having CeO2 as the nucleating layer tends to permit the formation of microscopic cracks that can limit the maximum Jc of the superconductor article or result in reliability problems during field use.
Epitaxial metal oxides on crystalline or polycrystalline metal surfaces have potential application in fields other than superconductors. Epitaxial metal oxides on crystalline metal surfaces may prove useful where thin epitaxial layers are needed in electronic applications. Furthermore, epitaxial oxide layers on polycrystalline metal surfaces have potential use in tribological or fuel cell applications where the properties of the metal/oxide interface largely determine material performance. For epitaxy on randomly-oriented polycrystalline metal surfaces, the epitaxial relationship involves a grain-by-grain registry of film and substrate crystallographic orientations.
An epitaxial article includes a substrate having a textured metal surface, a single lanthanum metal oxide epitaxial buffer layer disposed on and in contact with a surface of the substrate, and an electromagnetically active layer disposed on and in contact with the single epitaxial buffer layer. The lanthanum metal oxide epitaxial buffer layer can be selected from compounds having the general formula La1xe2x88x92xAxMO3, where A and M are metals and 0xe2x89xa6xc3x97xe2x89xa60.8. A can be Sr, Ba or Ca, while M can be Mn or Co. The buffer layer can have a resistivity of less than 1 mOhm-cm at 300 K, or more preferably less than 0.1 mOhm-cm.
The electromagnetically active layer preferably includes a superconducting layer, the superconductor layer being an oxide superconductor. The oxide superconductor layer can be REBa2Cu3O7 where RE is a rare earth element, Tl1Ba2Canxe2x88x921CunO2n+3, where n is an integer between 1 and 4, Tl2Ba2Canxe2x88x921CunO2n+4 where n is an integer between 1 and 4, or Hg1Ba2Canxe2x88x921CunO2n+2, where n is an integer between 1 and 4.
The textured substrate can be a rolled and annealed biaxially-textured metal substrate. The textured metal surface can be a metal selected from Cu, Cu-based alloys, Co, Mo, Cd, Pd, Pt, Ag, Al, Ni, and Ni-based alloys. Alternatively, the textured metal surface can be a metal selected from Ni or Ni-based alloys with at least one alloying agent selected from Co, Cr, V, Mo, W, and rare earth elements.
In an alternate embodiment of the invention, an epitaxial article includes a substrate having a textured metal surface, a lanthanum metal oxide epitaxial buffer layer disposed on and in contact with a surface of the substrate, and at least one epitaxial capping layer disposed on and in contact with the lanthanum metal oxide epitaxial buffer layer. The epitaxial capping layer is a different composition compared to the buffer layer. An electromagnetically active layer is disposed on and in contact with the epitaxial capping layer.
The epitaxial buffer layer can be selected from compounds having the general formula La1xe2x88x92xAxMO3, where A and M are metals and 0xe2x89xa6xc3x97xe2x89xa60.8. A can be Sr, Ba or Ca and M can be Mn or Co.
The electromagnetically active layer can include a superconducting layer. Preferably, the superconductor layer is an oxide superconductor. The oxide superconductor can be REBa2Cu3O7, where RE is a rare earth element, Tl1Ba2Canxe2x88x921CunO2n+3, where n is an integer between 1 and 4, Tl2Ba2Canxe2x88x921CunO2n+4, where n is an integer between 1 and 4, or Hg1Ba2Canxe2x88x921CunO2n+2, where n is an integer between 1 and 4.
The substrate can be a rolled and annealed biaxially-textured metal substrate. The metal textured surface can be a Cu, Cu-based alloy, Co, Mo, Cd, Pd, Pt, Ag, Al Ni, or a Ni-based alloy. The textured surface can be Ni or a Ni-based alloy with at least one alloying agent selected from Co, Cr, V, Mo, W, and rare earth elements. The epitaxial capping layer can be a rare earth oxide. The capping layer can be SRO, LNO, YSZ, CeO2 or Y2O3.
A method for preparing an epitaxial article, includes the steps of providing a substrate with a textured metal surface, depositing a single lanthanum metal oxide epitaxial buffer layer on and in contact with the surface of the substrate, and depositing an electromagnetically active layer on the single lanthanum metal oxide epitaxial buffer layer. Preferably, the substrate provides a biaxially-textured metal surface. The method can include the step of rolling and annealing a metal material to form a biaxially-textured substrate surface. Preferably, the metal rolled and annealed is Cu, Cu-based alloy, Co, Mo, Cd, Pd, Pt, Ag, Al, Ni, or a Ni-based alloy. If a Ni-based alloy is used, an alloying agent such as Co, Cr. V, Mo, W, and rare earth elements is preferably added.
The lanthanum metal oxide epitaxial buffer layer can have the general formula La1xe2x88x92xAxMO3, where A and M are metals and 0xe2x89xa6xc3x97xe2x89xa60.8. A can be Sr, Ba or Ca, while M can be Mn or Co. The lanthanum metal oxide epitaxial buffer layer can have a resistivity at 300 K of less than 1 mOhm-cm, or more preferably, less than 0.1 mOhm-cm.
The electromagnetically active layer can include a superconducting layer. The superconductor layer is preferably an oxide superconductor, the oxide superconductor layer being REBa2Cu3O7, where RE is a rare earth element, Tl1Ba2Canxe2x88x921CunO2n+3, where n is an integer between 1 and 4, Tl2Ba2Canxe2x88x921CunO2n+4, where n is an integer between 1 and 4, or Hg1Ba2Canxe2x88x921CunO2n+2, where n is an integer between 1 and 4.
The lanthanum metal oxide epitaxial buffer layer is preferably deposited by a sputtering process. The sputtering process can be rf-magnetron sputtering. The electromagnetically active layer can be deposited by a process of pulsed laser ablation, physical vapor deposition such as electron beam evaporation and sputtering, solution deposition and chemical vapor deposition.
A method for preparing an epitaxial article includes the steps of providing a substrate with a textured metal surface, depositing a single lanthanum metal oxide epitaxial buffer layer on the surface of the substrate, and depositing at least one epitaxial capping layer on the single lanthanum metal oxide epitaxial buffer layer. The epitaxial capping layer is of a different composition than the single lanthanum metal oxide epitaxial buffer layer. An electromagnetically active layer is deposited on the epitaxial capping layer.
The method can include the step of providing a biaxially-textured metal surface, preferably by rolling and annealing a metal material to form the biaxially-textured substrate. A metal substrate is preferably a Cu, Cu-based alloy, Co, Mo, Cd, Pd, Pt, Ag, Al, Ni, or Ni-based alloy. If a Ni-based alloy is used, alloying agents are preferably Co, Cr, V, Mo, W, or rare earth elements.
The Lanthanum metal oxide epitaxial buffer layer can be a compound having the general formula La1xe2x88x92xAxMO3, where A and M are metals and 0xe2x89xa6xc3x97xe2x89xa60.8. A can be Sr, Ba and Ca. M can be Mn or Co.
The electromagnetically active layer can include a superconducting layer, preferably an oxide superconductor. The oxide superconductor can be REBa2Cu3O7, where RE is a rare earth element, Tl1Ba2Canxe2x88x921CunO2n+3, where n is an integer between 1 and 4, Tl2Ba2Canxe2x88x921CunO2n+4, where n is an integer between 1 and 4 or Hg1Ba2Canxe2x88x921CunO2n+2, where n is an integer between 1 and 4.
The lanthanum metal oxide epitaxial buffer layer can be deposited by a sputtering process. The sputtering process is preferably an rf-magnetron sputtering process. The electromagnetically active layer is preferably deposited by a pulsed laser ablation process. The epitaxial capping layer can be SRO, LNO, YSZ, CeO2,Y2O3 or a rare earth oxide.
An epitaxial article can provide a foundation for applying electromagnetically active layers directly thereon, and include a substrate having a textured metal surface, and a single lanthanum metal oxide epitaxial buffer layer disposed on and in contact with the surface of the substrate. No additional buffer layer is required with this architecture. The lanthanum metal oxide epitaxial buffer layer can be a compound having the general formula La1xe2x88x92xAxMO3, where A and M are metals and 0xe2x89xa6xc3x97xe2x89xa60.8. A can be Sr, Ba or Ca. M can be Mn or Co.
A method for preparing an epitaxial article for applying electromagnetically active layers directly thereon includes the steps of providing a substrate with a textured metal surface and depositing a single lanthanum metal oxide epitaxial layer on the substrate. The metal surface is a preferably a biaxially-textured metal surface, formed by rolling and annealing a metal material. Metals such as Cu, Cu-based alloys, Ag, Al, Co, Mo, Cd, Pd, Pt, Ni, or Ni-based alloys are preferably rolled and annealed. If a Ni-based alloy is used, alloying agents are preferably Co, Cr, V, Mo, W, or rare earth elements.
The lanthanum metal oxide epitaxial layer can be a compound having the general formula La1xe2x88x92xAxMO3, where A and M are metals and 0xe2x89xa6xc3x97xe2x89xa60.8. The lanthanum metal oxide epitaxial layer can be deposited using a sputtering process. Preferably, the sputtering is rf-magnetron sputtering.
An epitaxial article includes a substrate having a metal surface, a single electrically conductive epitaxial buffer layer, and an electromagnetically active layer disposed on and in contact with the single epitaxial buffer layer, the buffer layer being substantially crack-free. The epitaxial buffer layer can be at least 100 nm thick without substantially cracking. The epitaxial buffer layer can have a resistivity at 300 K of less than 1 mOhm-cm, or more preferably less than 0.1 mOhm-cm. In the preferred embodiment, the electromagnetically active layer includes a superconducting layer.